This application relates to the retorting and recovery of liquid and gaseous products from subterranean deposits containing oil shale for the production of carbonaceous products including shale oil.
This application is also related to U.S. patent application Ser. No. 603,704, entitled "In Situ Recovery of Shale Oil" filed Aug. 11, 1975, now U.S. Pat. No. 4,043,595 by Gordon B. French. The disclosure of this latter application is hereby incorporated by reference.
The term "oil shale" as used in the industry is, in fact, a misnomer. It is neither shale nor does it contain oil. It is a sedimentary formation comprising marlstone deposits interspersed with layers containing an organic polymer called "kerogen" which upon heating decomposes to produce carbonaceous liquid and gaseous products. A variety of other minerals are contained in this deposit. It is the deposit containing kerogen that is called "oil shale" herein and the carbonaceous liquid product is called "shale oil".
One technique for recovering shale oil is to form an in situ oil shale retort in a subterranean deposit containing oil shale. A void is excavated within the site of an situ oil shale retort being formed. At least a portion of the deposit within the boundaries of the in situ oil shale retort site is explosively expanded toward the void to form a fragmented permeable mass of particles containing oil shale in the in situ oil shale retort. The fragmented mass is ignited near the top to establish a combustion zone and oxygen supplying gas is introduced in the top of the retort to sustain the combustion zone and cause it to advance downwardly through the fragmented permeable mass of particles in the retort.
As burning proceeds the heat of combustion is transferred by flowing gas to the fragmented permeable mass of particles containing oil shale below the combustion zone to release shale oil and gaseous products therefrom in a retorting zone. Thus, a retorting zone advances from top to bottom of the retort in advance of the combustion zone and the resulting shale oil and gaseous products pass to the bottom of the retort for collection and removal. Other retorting fluids such as preheated gas can be employed for retorting oil shale in the fragmented mass.
In preparation for the retorting process, it is important that the deposit containing oil shale be fragmented rather than simply fractured to create sufficient permeability that undue pressures are not required to pass gas through the retort. Otherwise, gas passed through the retort must have a high differential of pressure between the top and bottom, which consumes a large amount of power.
It is also significant that retorting gas be introduced to the top of the retort in a manner that minimizes channeling of gas flow through the fragmented mass in the retort. When a large area of oil shale, deposit is being exploited a comprehensive system of underground workings is desirable to permit access to the retorts being formed and the operating retorts for introduction of retorting gas, excavation of deposit to form voids, explosive expansion of deposit in the retort sites to form additional fragmented masses and for recovery of liquid and gaseous products from the retorts. Safety, convenience and economy of operation are considered.